This invention relates to conduit containment systems and more particularly to an improved duct system for containing and supporting pipes, conduits, cables and the like.
It is normal practice to support electrical cables and wiring systems, conduits, pipes, tubes and the like, hereinafter sometimes referred to collectively as conduits, in or on a continuous support system, particularly in large buildings and industrial installations. In the past, these systems have frequently been in the form of open racks or trays, usually referred to as ladders, with the conduits being supported on and secured to the cross members or rungs of the ladder. Such ladder structures conventionally have been constructed of metal, usually galvanized steel, although the use of lightweight metal extrusions and fiber reinforced plastic (FRP) materials have also been used. Examples of such ladders may be found in U.S. Pat. No. 3,791,613 to Nollen; U.S. Pat. No. 3,938,767 to Norris; U.S. Pat. No. 4,319,724 to Bradbury and U.S. Pat. No. 4,802,643 to Uys.
The open construction of the prior art ladder support systems inherently subjected the conduits to moisture and other corrosive substances, particularly in industrial applications, utility tunnels and the like and exposed the supported conduits to mechanical or physical contact and damage. Further, personnel and equipment may be exposed to electrical shock or to injury or contamination by dangerous fluids as a result of damage to cables or conduits supported by such open trays or ladders. Accordingly, safety regulations may require secondary containment for such conduits, particularly for high voltage cables or pipes containing steam or corrosive or hazardous fluids. While secondary containment systems provide increased safety over open ladder structures, known systems generally have not provided adequate corrosion or mechanical impact resistance and have not provided the desired protection from electrical shock or contamination. It is accordingly, a primary object of the present invention to provide an improved secondary containment system or duct for use as a secondary containment for such conduits to protect personnel and equipment from hazards resulting from damaged electrical conductors or fluid conduits supported in the system.
Another object is to provide an improved secondary containment system formed from an electrically insulating material which will provide maximum resistance to corrosion damage and protection from electrical shock.
Another object is to provide such a secondary containment system which provides a completely sealed duct for containing fluids or the like which might escape from damaged conduits within the system.
Another object is to provide such system produced from synthetic resin material including separately formed fiberglass reinforced plastic structural members and panel members rigidly assembled to form independent duct sections which are joined together in end-to-end relation to provide an elongated secondary containment system of any desired length.
Another object is to provide such a system having a removable top panel to provide convenient access to the interior of the system for repair and maintenance, with the top panel being outwardly convex to minimize collection and ponding of condensate or other fluids on the top cover.
Another object is to provide such a system made up of a plurality of end-to-end connected duct sections wherein individual sections may be removed to provide access to the conduits passing therethrough or to enable replacement of damaged duct sections.
In the attainment of the foregoing and other objects and advantages, an important feature resides in providing a duct system for secondary containment of fluid conduits, electrical cables or the like, and comprising a plurality of independent duct sections adapted to be connected in end-to-end relation. Each duct section includes a pair of elongated structural elements produced from fiber reinforced plastic (FRP) material, for example, glass fiber reinforced polyester or vinyl ester thermoset resins, produced by a pultrusion process to provide maximum resistance to corrosion and thermal shock and to withstand substantial mechanical impact. The two structural elements are identical and arranged in mirror image relation, one on each side of the duct. Each structural element has a substantially Z-shaped cross section including a generally planar central web defining one sidewall of the duct, an inwardly directed bottom leg or flange extending along the full length of the web at its bottom edge and an outwardly directed top leg or flange extending along the full length of the web at its top edge. A continuous slot or groove is formed in the inwardly directed edge of the bottom flange to provide a tongue and groove joint with the side edge of a generally rectangular flat bottom panel. The bottom panel may include a section of transparent plastic sheet to permit viewing the interior of the duct system through the bottom wall.
A top cover, preferably of fiber reinforced plastic sheet, extends over and closes the open top of the trough defined by the transparent bottom wall and the two structural side members. Insulative fastener members extending through the top flanges and the top cover rigidly, but removably, secure the cover in position. The top surface of the top flange is inclined downwardly slightly with respect to the plane of the open top, and the top panel is bowed or sufficiently flexible so that the fastener members draw its edge portions down into contact with the flanges causing the center of the top cover to bow upwardly and produce a naturally draining contour to eliminate any low spots which could collect condensate or other fluids. A suitable sealing gasket member is provided between the top cover panel and the top flanges to provide a fluid tight seal. Also, suitable means such as adhesive bonding and plastic riveting provide a fluid tight seal at the tongue-and-groove joint between the bottom flanges and the bottom panel.
Each section of the duct system is provided with an outwardly extending flange at each end, and through openings in the flange permit bolting of adjacent sections in end-to-end relation to form a duct of the desired length. Suitable gasket means are provided to form a fluid tight joint between adjacent sections in the assembled duct system. Bridge means extending between the two FRP structural members may also be provided at spaced intervals along the respective duct sections to support the weight of conduits within the system. Such bridge members may be a length of an extruded or pultruded FRP shape having its opposed ends connected one to the bottom flange on each FRP structural member.